Studies will be carried out to determine how progesterone (P) exerts potent antiinflammatory and immunosuppressive activity in vivo. Effects of P and other steroids on lymphocyte and microphage activation and functions will be studied in vitro. Selective effects on eosinophil, PMN, and monocyte chemotaxis will be sought. Experiments are also structured toward establishing human trophoblastic cell growth in rats treated with hormones. Finally, mechanisms that regulate progesterone synthesis by the human placenta will be investigated.